These samples will be analysed using quantitative cultures for the number of resistant organisms, and samples will be subject to quantitative real time PCR to quantify resistant genes (CTX-M, TEM, SHV, KPC, VIM as required). In parallel, environmental contamination will be examined and quantified using similar methods. Data will be collected daily regarding antibiotic treatment, other medications, clinical parameters, bowel movements and presence of diarrhoea, and various PK/PD indices. The target antibiotic for this study include commonly use agents in the hospital setting including quinolones, cephalosporins, piperacillin/tazobactam, ertapenem, imipenem, doripenem, metronidazole, clindamycin and aminoglycosides. The duration, the sequential order of treatment and PK/PD indices will be examined. The effects of surgical antibiotic prophylaxis will be examined as an important end point. The effects of the target antibiotic agents/classes on selection, enrichment, and spread of the target AMR organisms. Analyses will be conducted to compare: 1. the effects of various antibiotics 2. the effect of duration of therapy 3. the durability of the effect (posttreatment). 4. The effects of PK/PD indices.